1. Field of the Invention
The present invention relates to a multi-stage coil for a transformer which is formed by winding at least two or more flat rectangular electric wires in multiple stages and is used for a mold transformer, and to a winding method and apparatus for manufacturing the same.
2. Description of Related Art
Conventionally, there has been described an art in which in order to manufacture a multi-stage coil efficiently, a flat rectangular electric wire is rolled in a sheet thickness direction by paired pressure rollers by using motor power, and thereafter, the flat rectangular electric wire is wound concentrically to form an annular coil, and particularly, there has been stated that the above described paired pressure rollers are configured to be able to change the pressing angle of the flat rectangular electric wire in the sheet thickness direction in accordance with the radius of curvature of a curved portion of the coil (Japanese Patent No. 3996005). Further, as an art of manufacturing a winding coil of a flat conducting wire (flat rectangular electric wire) by using a round conducting wire with insulating coating, there has been described an art in which after a round conducting wire with insulating coating is passed between pressure rollers and deformed to be a flat conducting wire, the conducting wire is wound up in the form of a coil (JP-A-2000-69721).
In the art disclosed in Japanese Patent No. 3996005, the rolling is performed in accordance with a predetermined radius of curvature of the curved portion (corner portion) of the coil by changing the pressing angle of the pressure rollers against the flat rectangular electric wire. Therefore, when the radius of curvature is small, or the rolling deformation amount in the sheet thickness direction by the pressure roller is large, the insulating material such as an insulating sheet or an insulating film which is wound on the electric wire easily breaks at the time of rolling, and therefore, there is the fear of occurrence of short circuit and the like. Further, while the shape of the coil may change due to the inclination of the pressure roller, the pressing amount against the electric wire, the size variation of the electric wire material and the variation of a material characteristic such as malleability, it is difficult to modify the coil shape. Further, in the case of the art disclosed in JP-A-2000-69721, it is nothing but an art of providing a coil shape by automatically winding a flat conducting wire (flat rectangular electric wire) formed by rolling a round conducting wire with insulating coating, and there is the fear of easily causing breakage of the insulating coating, and reduction in conductor occupation rate and the like in the curve portion (corner portion) of the coil.
Thus, as an art of relating to an annular coil for a transformer and the like, and especially forming a curved portion such as a corner portion of the coil by deforming the sectional shape of the conductive element wire, there has been proposed, in connection with a coil element wire portion forming the curved portion of the annular coil, the coil element wire is rolled by a first roller so that the deformation amount of a portion near the outer peripheral side of the annular coil in its section is larger than that of a portion near the inner peripheral side to achieve bending deformation in the lengthwise direction, and thereafter, the above described element wire portion which is deformed in section is further deformed by being bent in the lengthwise direction by a second roller. In the annular coil used for a transformer or the like, breakage of the insulating coating and reduction in conductor occupation rate are prevented even in a curvilinear portion (curved portion) such as a corner portion of the annular coil so as to eliminate the breakage of the insulating coating and enable reduction of loss. There is proposed an annular coil, a coil manufacturing device, a coil manufacturing method and a transformer (JP-A-2006-196682).
In the art described in Japanese Patent No. 3996005, the corner radius is formed by rolling one flat rectangular wire in the sheet thickness direction by a forming roller, and a straight portion is formed by linearly feeding the flat rectangular wire after releasing rolling. That is, as a coil for a transformer, it is a single-wound coil. However, in order to increase the transformer capacity, increase in size of the flat rectangular electric wire used for a coil, in other words, the sectional area of a single wire is required. However, in the case of increasing the size in the case of the single wire, there is a limit in manufacturing, such as a technical problem in manufacturing the electric wire itself, cost, a technical problem of the manufacturing device itself such as a wire winding apparatus and the like.